Doctor back



June 11, 1968 D. B. DE NOVYER ETAL 3,387,317

DOCTOR BACK INVENTORS A/gyer C/arence 0. M-Abb Filed July 25, 19,66

% ATTORNEYS United States Patent 3,387,317 DOCTOR BACK Donald B. De Noyer and Clarence D. McNabb, Beloit, Wis., assignors to Beloit Corporation, Beloit, Wis., a corporation of Wisconsin Filed July 25, 1966, Ser. No. 567,730 2 Claims. (Cl. 15-25651) ABSTRACT OF THE DISCLOSURE The invention is directed to a doctor for scraping the surface of a roll of a paper making machine. The doctor includes a back adjacent the roll being scraped and extending along the axial length of the roll, the back is pivoted about an axis parallel to the surface of the roll so as to be selectively rotated about its axis toward and away from the roll surface. A scraping blade extends along the axial length of the roll and is engageable with the surface of the roll. A plurality of resilient rods are connected between the back and the blade to resiliently support the blade. Stop means are provided between the resilient rods and the back to limit the amount of resilient travel of the rods.

This invention relates generally to apparatus used in paper-making machines and, more particularly, the present invention relates to a doctor assembly which is used for scraping the surfaceof rolls in a paper-making machine.

The word doctor, as used in the paper-making industry, refers to a scraper that is used to keep the surface of a roll free from particles of paper stock which stick to the roll surface as the paper web passes over the roll. Also, the doctor may be used to scrape off and collect the wet broke from a top press roll. In some instances, the doctor is oscillated laterally with respect to the surface of the roll to prevent scoring of the roll surface by the doctor blade.

An object of the present invention is to provide a doctor blade assembly which is uniformly flexible along the axial length thereof.

Another object of the present invention is to provide the doctor blade with a positive stop position which will limit fiexion of the blade when an overload is caused by such particles as wads or paper wrap building up between the blade and the roll.

Another object of the present invention is to provide a doctor blade which is sufficiently flexible to permit the doctor blade to follow the contour of the roll associated therewith without having to bow the doctor back.

Another object of the present invention is to provide a doctor blade assembly which is substantially invariant to temperature changes, thereby maintaining substantially uniform pressure across the face of the roll.

Still another object of the present invention is to eliminate the accurate machining necessary on doctors having blade holders bolted or fixedly secured to the doctor back.

One of the features of the present invention is the use of a plurality of resilient rods secured at one end thereof and adapted at the other end thereof for receiving the doctor blade.

Another feature of the present invention is the use of a plurality of blade holders approximately one inch in length with a resilient rod connected to each holder. This feature provides uniform unit pressure between the doctor blade and the surface of the roll associated therewith.

Another feature of the present invention is the use of an actuating device which is connected to the doctor back to rotate the doctor back in either one of first and second directions about an axis, thereby providing a variable control of unit pressure between the doctor blade and the surface of the roll.

Still another feature of the present invention is the use of positive retainers or stops which are provided adjacent each end holder to permit lateral oscillation of the doctor blade across the surface of the roll, thereby to prevent scoring of the roll by the blade due to irregularities associated with the blade.

Briefly, the doctor assembly comprises a doctor back,

7 a blade holder, and a blade secured to the blade holder.

The blade is selectively engageable with the surface of a roll to scrape off particles adhering to the surface. A plurality of resilient rods is connected between the doctor back and the blade holder to apply uniform pressure to the blade as it is urged against the surface of the roll.

Other objects and features will be more fully realized and understood from the following detailed description when taken in conjunction with the accompanying drawing in which the single figure shows an elevational crosssectional view which is taken along a plane perpendicular to the axial length of the doctor assembly.

As seen on the drawing, a doctor assembly 10 is provided with a blade 11 which engages the surface of a roll 12. The blade 11 scrapes against the surface of the roll 12 to remove particles of paper stock which might stick to the roll surface as a paper web passes over the roll. Furthermore, the blade 11 may be used to scrape off and collect the wet broke from a top press roll of a papermaking machine.

A doctor back 13 is constructed from a pair of steel plates 14 and 16. The steel plate 14 has a bend 17 such that the steel plate 14 forms a rear wall 18 and a side wall 19. The steel plate 16 has a bend 20 to form a front wall 21 and a side wall 22. The steel plates 14 and 16 are welded together, as indicated by reference numerals 23 and 24, in such a manner as to form a chamber 26 within the doctor back 13.

A plurality of rods 27 is fixedly secured to the rear wall 18 and extends through the chamber 26 and through a plurality of openings 23 in the front wall 21. The opening 28 may be cut into the front wall 21 in such a manner as to form a plurality of spacers 28 between each of the rods 27. On the other hand, the openings 28 may be defined by inserting spacers at regular intervals along the length of a slot, thereby dividing the slot into a plurality of openings. A plurality of blade holders 29 is secured to the plurality of rods 27 exteriorly of the doctor back 13.

Each of the blade holders 29 has a notch 30 for receiving and holding the blade 11. A keeper 31 is fastened to the holder 29 by a screw 32. The rear portion of the keeper 31 engages a flange 33 which is formed on the blade 11 to retain the blade 11 in a fixed position.

Suitable end caps (not shown) may be provided at each end of the doctor 'back 13 to allow the doctor back to be pivoted about an axis 34 in either direction as indicated by the arrowed lines 36 and 37. A11 actuating device 38 is connected to the exterior surface of the rear wall 18 to selectively rotate the doctor back -13 about the axis 34. For example, should the doctor back '13 be pivoted in the direction indicated by the arrow 37, the blade 11 will be urged firmly against the surface of the roll 12 to scrape material therefrom.

To prevent overflexing of the rods 27 due to large clots or wads collecting between the blade 11 and the surface of the roll 12, a stop 40 is formed as an integral part of the doctor back 13. Therefore, the rods 27 will be flexed freely through the distance D, between the rods 27 and the seat 40, but when the rods 27 engage the seat 40, further flexion of the rods is prohibited.

When the blade 11 is inserted into the blade holders 29, it is necessary to align the blade holders to accommodate easy insertion of the rear portion of the blade through the notches 30. Therefore, to facilitate alignment of the blade holders a seat 11 is formed as an integral part of the doctor back, and which seat engages a boss 42 which is formed on each of the blade holders 29. By rotating the doctor back 13 in the direction indicated by the arrow 36, the seat 41 will engage all of the bosses 42 of the blade holders 29, thereby aligning the notches 30 for easy insertion of the blade 11.

In many instances it is desirable to oscillate the doctor assembly through a lateral movement so that the blade -11 is continuously wiped across the surface of the roll 12. To prevent lateral flexion of the rods 27 and maintain the blade holders in a fixed lateral position relative to the doctor back 13, a pair of retainers 43 is positioned at each end of the forward wall 21. The retainers 43 engage a portion of the end mounted blade holders 29 thereby causing the blade holders to move laterally with the doctor back.

In the preferred embodiment of the present invention, the center-to-center distance between the rods 27 is one inch, and the axial dimension of each of the rod holders 29 is one inch. Therefore, each of the rod holders 29 abuts against the adjacent rod holder to provide substantially continuous and uniform pressure to the blade 11 against the surface of the roll 12.

Therefore, the present invention has provided a new and improved doctor assembly for scraping the surface of a roll. The doctor back of the present invention provides flexibility with rods which act as spring loading and which rods have a positive stop to limit the flexion thereof when an overload caused by a wad or paper wrap becomes lodged between the blade and the surface of the roll. Also, the present invention provides sufficient flexibility to permit the doctor blade to follow the contour of a crowned roll Without having to bow the doctor back. The flexibility is of such a degree that distortion due to temperature change will cause only a small change in unit pressure across the face of the roll. Furthermore, the present invention eliminates the accurately machined surfaces necessary on doctor assemblies having the blade holder bolted or fastened rigidly to the doctor back. Additionally, uniformity of unit pressure is accomplished by providing blade holders 29 with an axial length of one inch and with a resilient rod to each of such holders. Therefore, the blade 11, which is a continuous blade across the surface of the roll, will be subjected to pressure from each of the rods along the axial length of the blade. Variations in unit pressure may be accomplished by energization of the actuator 38 so as to rotate the doctor back 13 about the axis 34.

An alternate arrangement of the blade holders 29 and rods 27 is to extend the axial length of each blade holder so as to receive two or more of the rods 27. This type of arrangement would decrease the flexibility of the assembly, but would offer lower cost construction and easier assembly on applications that do not require a maximum of flexibility.

It will be understood that other variations and modifications may be effected without departing from the spirit and scope of the novel concepts of this invention.

We claim as our invention:

1. In a paper making machine, a doctor for scraping the surface of a roll, comprising:

a back adjacent said roll and extending along the axial length of the roll, said back pivoted about an axis parallel to the surface of said roll to be selectively rotated about said axis in first and second directions;

a blade extending along the axial length of sa d roll and selectively engageable with the surface of said roll;

resilient means connecting said blade to said back;

said resilient means including a plurality of spacedapart resilient rods, each having one end thereof fixedly secured to said back and the free end thereof extending toward the surface of the roll; a blade holder secured to said free end of each of said rods; a boss formed on each of said blade holders and extending toward said back; and a seat formed by a portion of said back, where-by rotation of said back in said second direction will cause said seat to engage said bosses to align said blade holders;

whereby rotation of said back in said first direction about its axis will cause said blade to be urged against the surface of said roll by pressure from said resilient means.

2. The apparatus of claim 1 wherein said resilient means includes a plurality of spaced-apart resilient rods, each having one end thereof fixedly secured to said back and the free end thereof extending toward the surface of the roll; a blade holder secured to said free end of said rods; a boss formed on each of said blade holders and extending toward said back; a seat formed by a portion of said back for engaging said boss to align said blade holder; and retainer means secured to said back adjacent said blade holders and in abutting relation with the portion of the end-mounted blade holders to retain said blade holders in a lateral alignment with respect to said back.

References Cited UNITED STATES PATENTS 2,191,366 2/1940 Buccicone et a1. 15-256.51

2,576,633 11/1951 Naylor 15256.5l X

2,732,773 1/1956 Smith 15256.53

FOREIGN PATENTS 1,112,391 8/1961 Germany.

CHARLES A. WILMUTH, Primary Examiner.

LEON G. MACHLIN, Examiner. 

